Intl.DateTimeFormat

[TorsteinHonsi]

Implemented locale-aware datetime formats through the Intl.DateTimeFormat browser API. All default time formats are now respecting the browser locale.

This PR is related to the Time refactor PR, but with different concerns:

• The Time refactor PR replaces all internal time zone handling with functions powered by Intl.DateTimeFormat
• The Intl.DateTimeFormat opens up for using locale and DateTimeFormatOptions in Highcharts options.

To do

• Decide where to set the locale option. Probably best as chart.locale.
• Align the locale option with Intl. In type definitions, allow arrays and instances of Intl.Locale.
• Add object defaults for all other time definitions except those of a non-locale nature like %Y-%m-%d.
• Implement caching for DateTimeFormat instances.
• Handle capitalization for standalone formats like x-axis labels and tooltip headers. Could be a custom option on the extended Intl.DateTimeFormatOptions. Or maybe a templating helper. Axis and current-date done via the simple call to Time.dateFormat. But tooltips need to be handled another way through a sentenceCase custom property, and abstraction of Intl.DateTimeFormat.
• Handle extended or concatenated formats lik "Week from Monday, ..." and the to formats. Consider a custom prefix option on Intl.DateTimeFormatOptions. Which means we would need our own Time.DateTimeFormatOptions that extends Intl.
• Consider template keys for the most common ones.
• Consider localized defaults for lang.months, lang.weekdays etc. Will fix demos like gantt/current-date-indicator/demo.
• Separate error handling between bad timezone and bad config, see comment.

[highsoft-bot]

File size comparison

Sizes for compiled+gzipped (bold) and compiled files.

	master	candidate	difference
highcharts.js	95.8 kB 270.0 kB	96.1 kB 271.1 kB	248 B 1059 B
highstock.js	128.7 kB 371.7 kB	129.0 kB 372.9 kB	290 B 1186 B
highmaps.js	121.9 kB 349.8 kB	122.1 kB 350.8 kB	247 B 1059 B
highcharts-gantt.js	133.9 kB 385.7 kB	134.2 kB 386.9 kB	309 B 1257 B
dashboards/dashboards.js	43.2 kB 148.6 kB	43.3 kB 149.3 kB	149 B 693 B
datagrid/datagrid.js	24.8 kB 76.9 kB	24.9 kB 77.6 kB	150 B 693 B

[highsoft-bot]

Visual test results - Differences found

Found 338 diffing sample(s). Please review the differences.

---

Samples changed

Change type	Sample
Modified	samples/highcharts/studies/intl-datetimeformat/demo.js
Modified	samples/highcharts/studies/intl-datetimeformat/demo.js
Modified	samples/highcharts/studies/intl-datetimeformat/demo.js
Modified	samples/highcharts/studies/intl-datetimeformat/demo.js
Modified	samples/highcharts/studies/intl-datetimeformat/demo.js

[highsoft-bot]

Benchmark report - Stock

benchmarks/Stock/Stock-Base.bench.ts

Sample size	This PR avg (ms)	master avg (ms)	Diff	Percent diff
1000000	6323.64	6269.48	54.16	1%

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Sample size	This PR avg (ms)	master avg (ms)	Diff	Percent diff
1000	265.92	260.38	5.54	2%
10000	355.11	354.48	0.63	0%
100000	916.24	906.97	9.27	1%
1000000	6323.64	6269.48	54.16	1%

benchmarks/Stock/Stock-Ordinal.bench.ts

Sample size	This PR avg (ms)	master avg (ms)	Diff	Percent diff
1000000	1427.44	1393.22	34.22	2%

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Sample size	This PR avg (ms)	master avg (ms)	Diff	Percent diff
1000	267.48	260.96	6.53	3%
10000	285.55	273.94	11.61	4%
100000	516.54	494.11	22.43	5%
1000000	1427.44	1393.22	34.22	2%

benchmarks/Stock/Stock-DataGrouping-Ordinal.bench.ts

Sample size	This PR avg (ms)	master avg (ms)	Diff	Percent diff
1000000	1427.82	1412.66	15.16	1%

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Sample size	This PR avg (ms)	master avg (ms)	Diff	Percent diff
1000	270.61	274.5	-3.88	-1%
10000	292.96	281.76	11.2	4%
100000	503.68	499.85	3.83	1%
1000000	1427.82	1412.66	15.16	1%

benchmarks/Stock/Stock-DataGrouping.bench.ts

Sample size	This PR avg (ms)	master avg (ms)	Diff	Percent diff
1000000	1046.93	1037.81	9.12	1%

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Sample size	This PR avg (ms)	master avg (ms)	Diff	Percent diff
1000	252.47	249.58	2.89	1%
10000	272.7	258.85	13.85	5%
100000	401.09	383.08	18.01	5%
1000000	1046.93	1037.81	9.12	1%